1. Field of the Invention
The present invention relates to a supporting structure for a repeller and to an ion generator using the supporting structure.
2. Description of the Related Art
In a semiconductor manufacturing process, a process of implanting ions into a semiconductor wafer has been implemented on a standard basis for the purpose of changing conductivity, for the purpose of changing a crystal structure of the semiconductor wafer, and for some other purpose. An apparatus used in this process is generally called an ion implanter.
As an ion source in such an ion implanter, a direct current (DC)-discharge type ion source is known. A DC-discharge type ion source heats a filament by a current to generate thermal electrons, which then heat a cathode. Thereafter, thermal electrons generated by the heated cathode are accelerated by a DC voltage within an arc chamber and collided with source gas molecules therein, so that atoms included in the source gas molecules are ionized.
At a position opposite to the cathode in the arc chamber is provided a repeller that repels electrons accelerated within the arc chamber. The repeller is electrically insulated from the arc chamber, so as to have the function to repel electrons, improving the ionization efficiency within the arc chamber. The repeller is installed via an insulation member provided within the arc chamber, for example.
For the source gas molecules to be introduced into the arc chamber, a halide such as a fluoride or a chloride is often used. The source gas molecules of a halide generate halogen radicals in an ionization step, and the halogen radicals act on a component constituting the ion source, such as a metal material for an inner wall of the arc chamber, to form a chemical bond. The chemically-bonded metal material is then ionized with the source gas molecules and deposited as an ionized substance on the inner wall of the arc chamber or the like, which may form a conductive film.
When a metal material is deposited on the insulation member of the repeller as the ion source is used and when a conductive film is then formed, the insulation properties of the repeller are degraded. When the insulation properties are degraded, the repeller's function to repel electrons is significantly degraded, so that the generation efficiency of ions is lowered and the life of the ion source is shortened. As a result, the components with degraded insulation properties are replaced more frequently, causing deterioration of productivity in the process using the ion implanter.